The present invention relates to symbol reading techniques, and more particularly, to an improved laser source assembly used in a symbol reading device such as a barcode scanner.
As illustrated in FIG. 1, in an existing laser source assembly 100, a laser beam 30a is generated by a laser source such as a laser diode 10 and is then focused by a lens 20 to form a focused laser beam 30b to be projected onto a symbol or barcode (not shown) during a scanning operation. For obtaining a precise scanning result, it is critical to keep the laser source 10 and the focusing lens 20 at a predetermined precise distance so that the laser beam 30a is kept properly focused. Conventionally, to avoid the difficulties in adjusting the distance between the laser diode 10 and the lens 20 to the predetermined value, the laser diode 10 and the lens 20 are mounted (e.g., by tight fit) to an inner wall of a case 40 formed with two shoulders 41 and 42, as illustrated in FIG. 1. In particular, the two shoulders 41, 42 are apart from each other by a longitudinal distance exactly equal to the predetermined distance required between the laser diode 10 and the lens 20. When secured in place, the base 21 of the lens 20 abuts on the shoulder 41 while the base 11 of the laser diode 10 abuts on the shoulder 42, thus being spaced by the predetermined distance. To realize precise configurations, the case 40 is preferably a single die cast piece of a metal alloy such as a Magnesium, Iron, Nickel or Cobalt alloy.
However, when the ambient temperature changes, the case 40 made of the above metal alloys expands or shrinks, causing a change in the distance between the shoulders 41 and 42. This results in a change of the distance between the laser diode 10 and the focusing lens 20, which degrades the precision of the laser source assembly.